HSP90 inhibits apoptosis and promotes growth by regulating HIF-1α abundance in hepatocellular carcinoma.

Heat shock protein (HSP)90 functions as a general oncogene by targeting several well-known oncoproteins for ubiquination and proteasomal degradation. However, the clinical significance of HSP90, as well as the mechanisms responsible for the tumor-promoting effects of HSP90 in hepatocellular carcinoma (HCC) remain unclear. In this study, HSP90 and hypoxia-inducible factor (HIF)-1α expression in 60 samples of HCC tissues and matched normal tumor-adjacent tissue were assessed using immunohistochemistry (IHC) or western blot analysis. Flow cytometry, BrdU cell proliferation assay, caspase-3/7 activity assay and MTT assay were used to detect the apoptosis and proliferation of the HCC cells. The regulatory effect of HSP90 on HIF-1α in the HCC cells was confirmed by immunofluorescence staining, western blot analysis and RT-qPCR. The interaction between HIF-1α and HSP90 was analyzed by co-immunoprecipitation. A subcutaneous tumor xenograft model in nude mice was established and TUNEL assay was performed to evaluate cancer cell apoptosis and growth in vivo. We found that HSP90 expression was higher in the HCC tissues than in the normal tissues and that a high HSP90 expression correlated with poor clinicopathological characteristics, including venous infiltration, an advanced TNM stage and high pathological grading. Furthermore, we confirmed that patients with a negative expression of HSP90 had an improved 3-year survival, and that HSP90 was an independent factor for predicting the prognosis of patients with HCC. We demonstrated that HSP90 promoted HCC by inhibiting apoptosis and promoting cancer cell growth. Pearson's correlation coefficient analysis indicated that HSP90 expression positively correlated with HIF-1α protein expression in the HCC tissues. Furthermore, we found that HSP90 regulated HIF-1α protein abundance by inhibiting the ubiquitination and proteasomal degradation of HIF-1α in HCC cells. Additionally, the upregulation of HIF-1α expression partially abrogated HSP90 siRNA-induced HCC cell growth arrest and apoptosis in vitro and in vivo. These results indicate that HSP90 may be used as a prognostic marker and that HIF-1α may be one of the potential therapeutic targets of HSP90 in HCC.